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Penicillin, Amoxicillin: Step Aside for Strep Throat Treatment

December 19, 2005

Doctors have presented more evidence that it’s time for long-time antibiotic stalwarts like penicillin and amoxicillin to step aside when it comes to the treatment of strep throat.

The most common medications used to treat the strep germ, the bug that causes millions of sore throats in U.S. children every year, simply aren’t doing the job and aren’t as effective as newer antibiotics known as cephalosporins. In results presented this weekend at a large infectious disease meeting, the annual Interscience Conference on Antimicrobial Agents and Chemotherapy in Washington, doctors who reviewed the treatment given to 11,426 children showed that even a short course of the newer drugs is more effective than the traditional 10-day dose of the older antibiotics.

Pediatricians at the University of Rochester Medical Center found that 25 percent of children treated for strep throat with penicillin ended up back in the doctor’s office within three weeks of treatment. Children treated with amoxicillin returned 18 percent of the time. The numbers were 14 percent for older-generation cephalosporins, and just 7 percent for newer ones like cefpodoxime and cefdinir, which are given for just four or five days.

The new results buttress previous work by physicians Michael Pichichero, M.D., and Janet Casey, M.D., showing that more children who receive the older drugs relapse, prolonging their illness and forcing doctors to turn to even stronger drugs. Yet, said Pichichero, doctors across the land continue to prescribe ineffective medications. Studies have shown that approximately 60 to 80 percent of children treated for strep are prescribed amoxicillin; 10 to 20 percent are prescribed penicillin; and just 10 to 20 percent receive a cephalosporin.

“Most doctors are shocked to learn of the high failure rates of the older medications,” said Pichichero, a professor of Microbiology and Immunology.

“The treatment paradigm for treating strep sore throats has been changing slowly, and endorsing the use of cephalosporins as a first-line treatment is something that needs to be seriously considered,” Pichichero said.

While the newer short-course cephalosporins are only available in brand-name form and are much more expensive, older ones such as cephalexin (better known as Keflex) cost about the same as penicillin or amoxicillin but are more effective against strep.

Nearly all drugs fail some of the time, Pichichero said, and doctors accept some risk of failure as a trade-off for other factors like convenience, cost to families, and likelihood that a less powerful medication can kill the bug just as well as a more powerful drug. In the case of throat infections, doctors try to preserve their strongest antibiotics for the most severe cases. But most doctors would view a drug that fails in one out of four patients, as penicillin does in strep cases, as unacceptable, Pichichero said.

To understand why the older drugs don’t work as well, consider a child’s throat as a battleground for many types of bacteria vying for dominance. Repeated exposure to penicillin and amoxicillin shifts the center of microbial power, resulting in a throat full of bacteria that actually shield strep germs from the older drugs. At least four types of bacteria that Pichichero called “co-pathogens” become more dominant in the throat of someone who has received the drugs frequently. It happens in much the same way that the hardened thugs who protect a mob boss are chosen: The best henchmen are those who have survived multiple attempts on the boss’s life and have become experts at snuffing out future attacks, providing the boss immunity against threats that once were formidable.

The new results are an extension of a report last year in Pediatrics by Pichichero and Casey, who is clinical associate professor of pediatrics at Golisano Children’s Hospital at Strong. There they reported the waning effectiveness of penicillin and amoxicillin. This week they presented results of a meta-analysis of 47 studies from the past 35 years that had looked at the effectiveness of various drugs on treating strep in children. They found that four or five days of the newest cephalosporins were more effective than any other drug, failing at half the rate of older cephalosporins and less than a third the rate of penicillin.

The new findings are crucial not only for the children treated, but for their friends. Pichichero said children and parents are much more likely to adhere to taking all the prescribed medication in four or five days rather than 10 days. He noted that other studies have found that anywhere from 30 to 70 percent of parents make the mistake of discontinuing antibiotic medication for their children prematurely, or giving them leftover medication later on. Sometimes it’s just a misinformed attempt to give children less medication, but more often parents believe the drugs are no longer needed since the children are feeling better, despite the medication label that urges parents to make sure the child finishes all the medications.

The good intentions directly lead to children becoming sick on and off for weeks or months, as the strep germ isn’t quite killed off but instead lingers in the child’s body. The children also become vulnerable to much more severe infections that will demand the use of even stronger drugs later on. All the while, the still-contagious child is exposing his or her friends to strep.